The ability to accurately predict the effects of disease and treatment on an individual?s ability to function relies entirely on our capacity to understand the complex process that transforms muscular effort into functional movements. The overall purpose of this protocol is to extend existing human movement analysis methodologies and our understanding of movement activities by developing and applying analytical techniques that can provide direct estimates of the influence muscular effort and assistive technologies have on the movement of all joints, body segments, and overall functional movement task performance. Dynamic Bracing A variety of disorders and diseases affecting muscle and nerve function can cause sufficient lower extremity weakness to impact gait. Frequently these individuals are prescribed orthotic devices to assist their ambulation. A method for determining the stiffness of a commercially available (carbon fiber) ankle foot-orthosis has been developed. Preliminary studies indicate the deformation patterns of the carbon fiber ankle foot-orthosis during bench testing and wear during gait are congruent. Therefore, the stiffness characteristics obtained during bench testing are valid for the determination of orthosis generated moments while worn during gait. In addition, a method based on induced acceleration analysis has been used to determine the source of forces that load (bend) the carbon fiber ankle foot-orthosis during the dorsiflexion period of the stance phase of gait. We have used these analysis methods to study the contribution of existing dynamic AFOs on the walking patterns of patients with post-polio syndrome. Work has also begun on the development of a scaled relational gait database from instrumented gait analysis using normal subjects. The gait database is a critical component in a proposed AFO stiffness selection process. To date, motion capture data have been collected on 10 normal subjects walking at five scaled (relative to standing height) walking velocities. The natural ankle stiffness values obtained from the database will be studied to predict optimal AFO design characteristics as a function of body weight and targeted walking velocity. The Impairment Compensation Relationship Understanding the process and governing principles that links impairment to functional movement limitations, and ultimately disability, is one fundamental goal of rehabilitation and geriatric research fields. Impairments may cause inability to perform specific body functions, resulting in disability, when physiological reserve is markedly reduced and an individual cannot devise successful compensatory strategies. In order to assess the association among subject?s functional status and the role and effectiveness of compensatory movement strategies, we studied data from 131 elderly subjects, divided into five functional groups, who performed an experimental sit-to-stand (STS) paradigm. Results of this study clearly show that a hierarchy of compensatory movement strategies exists, in which the effectiveness of each strategy to maintain standing ability is strongly influenced by both the individual?s general functional status and the difficulty of the sit-to-stand task. As the functional status of the subject declines, so does the effectiveness of compensatory movement strategies. In a related study, we used a novel approach to identifying the motor strategies adopted for the execution of a sit-to-stand motor task, followed by the maintenance of the upright posture, in a sample of hemiparetic stroke patients. Beginning by the recording of external forces only, and using a musculoskeletal system model, based on a telescopic inverted-pendulum (TIP) moved by a linear and two rotational muscle-equivalent actuators, we extracted parameters describing the kinematics and dynamics of these actuators during a sit-to-stand task. The motor act, involving both dynamic and static balance control, and we used the TIP model to interpret the ground reactions data. The result indicated the TIP model and simplified data capture scheme have the capacity to discriminate movement alterations, the consequent functional limitations, and level of disability in stroke patients. Induced Acceleration Analysis By studying the contribution of net joint moments and individual muscle forces to control human movement and the performance of activities of daily living, we intend to link the capabilities of a physically challenged person to his or her ability to perform activities of daily living. Measuring these contributions is critical for defining adaptive movement control strategies, understanding the process whereby the strategy of movement control is selected and implemented, and determining the contribution assistive technologies play in enhancing function. We have further extended our models to estimate the source of mechanical energy exchange between segments and used it to determine the muscle groups responsible for the inter-segment transfer of mechanical energy during gait. We found that the energy transfer depends on the sign of the joint moment, rather than on the sign of the joint power and that pairs of net joint moments function in combination to balance energy flow through the leg and trunk segments during normal gait. Movement Visualization and Analysis for Rehabilitation Plotting kinematic and kinetic data of a patient?s movement patterns relative to normative values is a common method used by clinicians to visually assess deviations and interpret the patient?s gait analysis data. This method of data interpretation is often time consuming and complex, especially when the process requires the inspection of a plethora of line graphs for numerous variables that are displayed across several report pages. In collaboration with the University of Delaware, we have developed an alternate method for displaying movement pattern deviations relative to normative data by color-coding the magnitude and the direction of the deviation. The process effectively transforms the ordinate scale to a uni-dimensional color map. An advantage of this approach is that a single page summary of all the deviation magnitudes can be displayed simultaneously, in a manner that is concise, visually effective and reduces complexity. Accuracy and Reliability of Movement Analysis Techniques The percutaneous skeletal tracker (PST) is a device designed by Dr. Stanhope to achieve minimally invasive skeletal fixation of kinematic targets to human limbs. The PST enables us to measure actual bone movement and compare it directly to motion measured simultaneously using surface mounted targets. An important finding was the determination that optimal surface mounted target attachment techniques are incapable of locating proximal tibial position with sufficient accuracy to measure strain on joint structures such as the anterior cruciate ligament. A powerful technique for simultaneously evaluating the performance of all components of a clinical movement analysis laboratory has been developed and tested. The Commission for Motion Laboratory, Inc. recently endorsed use of this technique by clinical movement analysis laboratories seeking accreditation. The method has been implemented by C-motion, Inc. in the program CALtester and the testing device is currently distributed by Motion Lab Systems